IV. CAPACITY CONTROL (576B120 Only)
A suction
A. Control Set Point
The control set point (cylinder load point) is adjustable from 0 to 85 psig (586 kPa). To adjust, turn control set point ad- justment nut (Fig. 13) clockwise to its bottom stop. In this position, set point is 85 psig (586 kPa). Then, turn adjust- ment counterclockwise to desired control set point. Every full turn counterclockwise decreases set point by 7.5 psig (51.7 kPa).
B. Pressure Differential
The pressure differential (difference between cylinder load and unload points) is adjustable from 6 to 22 psig (41.4 to 152 kPa). To adjust, turn pressure differential adjustment screw (Fig. 13) counterclockwise to its back stop position. In this position, differential is 6 psig (41.4 kPa). Then, turn adjustment screw clockwise to desired pressure differential. Every full turn clock- wise increases differential by 1.5 psig (10.3 kPa).
Fig. 13 Ð Compressor Capacity Control Unloader
V. COMPRESSOR REMOVAL
See Tables 1A and 1B for compressor information.
Follow safety codes and wear safety glasses and work gloves.
1.Shut off power to unit. Remove unit access panel (front of unit).
2.Remove refrigerant from system using refrigerant re- moval methods described in GTAC II, Module 5, Charg- ing, Recovery, Recycling, and Reclamation.
3.Disconnect compressor wiring at compressor terminal box.
4.Remove bolts from suction ¯ange and discharge serv- ice valve (576B Units).
CAUTION: Excessive movement of copper lines at compressor may cause higher levels of vibration when unit is restored to service.
5.Remove crankcase heater from compressor base (576B units only).
6.Remove compressor holddown bolts.
7.Remove compressor from unit.
8.Clean system. Add new liquid line ®lter drier.
9.Install new compressor in unit.
10.Connect suction and discharge lines to compressor. En- sure that compressor holddown bolts are in place.
11.Connect wiring.
12.Install crankcase heater.
13.Evacuate and recharge unit, per Step VII.
14.Restore unit power.
VI. CRANKCASE HEATER (Except 569C072)
The crankcase heater prevents refrigerant migration and com- pressor oil dilution during shutdown when compressor is not operating.
Close both compressor service valves if applicable when crank- case heater is deenergized for more than 6 hours.
VII. REFRIGERANT CHARGE
Unit panels must be in place when unit is operating during charging procedure. Unit is shipped with a holding charge only. Weigh in 7 lbs (3 kg) of
See Troubleshooting Guide on page 14 for additional information.
A. Low Charge Cooling
Using Cooling Charging Charts, Fig. 14 and 15, vary refrig- erant until the conditions of the appropriate chart are met. Note the charging charts are different from type normally used. The charts are based on charging the units to the correct sub- cooling for the various operating conditions. Accurate pres- sure gage and temperature sensing device are required. Con- nect the pressure gage to the service port on the liquid line service valve. Mount the temperature sensing device on the liquid line, close the liquid line service valve, and insulate it so that outdoor ambient temperature does not affect the read- ing.
Operate unit a minimum of 15 minutes. Ensure that tem- perature and pressure have stabilized. Plot liquid pressure and temperature on chart and add or reduce charge as re- quired. Do not vent refrigerant to the atmosphere. Recover any excess charge. Operate the unit until the system stabi- lizes. Adjust charge to conform with charging chart, using liq- uid pressure and temperature to read chart.
B. Refrigerant Leaks
Proceed as follows to repair a refrigerant leak and to charge the unit:
1.Locate the leak and ensure that refrigerant system pres- sure has been relieved.
2.Repair leak following accepted practices.
NOTE: Install a new ®lter drier in the liquid line whenever the system has been opened for repair.
3.Add a small charge of
4.Evacuate refrigerant system if additional leaks are not found.
5.Charge unit with
NOTE: Do not vent refrigerant to the atmosphere. Recover any excess charge.
VIII. REFRIGERANT SERVICE PORTS
Each unit has 3 service ports: one on the suction line, one on the liquid line, and one on the compressor discharge line. Be sure caps on the ports are tight.
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